How do you turn teeny, tiny trees in pots into big, tiny trees in pots

I’ve been pouring myself into bonsai the past few months and I’m loving every minute of it, but I need a little help with some fundamentals.
The more I learn, the more I realize I just need to grow my trees and establish a baseline of health (balance of water and oxygen) before I start making big changes. I was getting ready to buy a bunch of root control pots and root control bags and then I thought maybe I’m making things too complicate, i.e. maybe I should just lift from the ground every few years and prune the roots.
If you had 20 or 30 trees all less than ten years old, that have been in pots since they were a 4” start, what would you do to get them headed on the path towards bonsai?
Plant them in the ground a la Telperion? Keep them in pots but change the soil mix so it’s much more freely draining? Prune the roots every year? Basic wiring for movement?
Help! I’m drowning in knowledge.
There is A TON of knowledge on this site but not much of it is geared towards seedling/sapling evolution…

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Hey Noah. Welcome!

I’m in a fairly similar situation, having started bonsai at the beginning of 2020. One thing I’ve learned is that seedlings don’t need fancy bonsai soil (akadama, pumice, etc). Seedlings should be kept in a relatively small, well-draining container in organic soil. If the container is too large, the soil will hold tons of water, and the tiny root mass will never have to work/grow to obtain nourishment. It will just be a lazy little plant and not grow new roots, or it will grow one super-long straggler root.

The small container will assure the water will get used by the plant and evaporate at a reasonable pace, allowing air into the environment, encouraging the roots to grow to seek more nourishment. When the goal is specifically to grow roots fast, you really want to lean on the “oxygen” part of the “water and oxygen” balance. To that end, you can search the internet for “air pots”, which will have a variety of grids/slots/holes to increase aeration.

When I started growing some Chinese elm seedlings, I put them straight into nice, smallish (~3" diameter, 3" height), glazed ceramic pots my wife made, with an organic-blend bonsai soil (some peat moss and compost mixed with pumice and, I believe, turface). Well, the seedlings grew but were not very happy. I decided recently to transfer them to some air pots with a regular organic nursery soil.

In the glazed ceramic pots, I had been watering these little guys roughly once a week, when the top of the soil began looking a little dry. However, when I dug the seedlings out to repot them, I saw that the vast majority of the organic bonsai soil mix was quite damp! After a week! On top of that, the plants had grown virtually no new roots. Terrible.

Obviously there was a big imbalance of water and oxygen (basically, not nearly enough oxygen). I just repotted these seedlings in the new air pots this week, but I can already see the soil becoming substantially drier after a few days, so I have high hopes that I’m starting a positive new cycle for them. Another awesome thing about these particular air pots is they have tiny vertical fins inside the pot to encourage downward root growth rather than pot-spiraling growth. Here’s a photo of root growth from the Amazon page (pretty intense!):

Once you get this kind of root growth going, the plant is thriving and the world is your oyster. Want more growth? Get a bigger air pot, or, sure, plant them in the ground for a while.

Obviously I’m a newbie, but I wanted to share my recent experience. Avoid anything approaching a bonsai pot and bonsai soil for very young plants, if your goal is to grow the plants.

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If you decide to plant in the ground I recommend the grow bags to keep a compact root ball instead a few roots that get big and run a long way. I develop stock in boxes with 3 mm screen bottoms. I used to use an inorganic mix in the boxes, but went to about 60% organic and 40% pumice this year. The goal of that is strong growth, but a root system that is easier to untangle and prune when repotting/transplanting than a straight organic mix.

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Thank you so much for the thoughtful reply!
It sounds like maybe I should just plant them in the ground. I’ve been making and using all my own pots for the garden out of hypertufa for the past five years or so (I like having all the pots look the same, it quiets my mind…) and I don’t really like the idea of looking at plastic pots every day even though those root control pots look like they work amazingly well.
Matching the pot size to the plant though is something I need to work on.
Regarding soil…fortunately I’m a cheap ass so I would never use akadama for anything but a tree that was actually in development. My thought was potting soil and pumice (until they’re big enough to go in the ground).

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Thanks for the reply. Is that a ratio you’d recommend in a root control bag as well (60/40)?

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Never heard of them being called air pots. Another name for them is root maker pots. I use various techniques because I’m curious and want to see what works best. I even have a tree in the ground in a root maker pot because I wanted the benefits of ground growing and the benefits of the root maker. :man_shrugging:t4:

I have trees in pond baskets which are basically cube shaped colanders. I also have trees in colanders. I’ve got trees in various sizes of grow bags. I’ve got trees in grow bags with the tops being air layered because why just chop the top off when you can make a raft out of the top? I’ve got trees that were collected…from the curb. Trees that I collected from the ground. Trays that started out as a bunch of seeds and may the strongest survive to make a forest. Nursery stock. Clearance rack stock. Common denominator is time…

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I’m planning to use the same 60 organic/40 pumice mix in the grow bags in the ground. The mix in the pots was actually 40% 1-9 mm bark, 40% 1-9 mm pumice, and 20% potting soil which I think contains peat since I decided I needed some finer stuff in the 5 - 20 cm pots. Last year’s mix in the grow bags was 50/50 garden soil (<12 mm) and diatomaceous earth (floor/oil dry in the 1 - 6 mm range).

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Ryan just mentioned in the last Live Q&A that he’s more a fan of Anderson flats than the root maker pots. Reason being that the root makers promote downward root growth whereas the flats promote lateral root growth which is more usable for bonsai development and leads to better nebari development. Okay, I’m interjecting the nebari thing, but still. I haven’t found a good source for Anderson flats, but I do build my own with 2x4’s. For my smaller trees (read: twigs :laughing:) I’m going to start cutting the pond baskets down by 50%-70% to create a shallower container.

Hi @Noah I have been using air pots for eight years now and I can tell you they are fantastic. Normally in any given year you can get two years of growth compared to an ordinary plant pot. I also grow a lot in the ground so can compare.
As an example I have grown a japanese larch from seed and just four years later it was styled as a shohin with a trunk of 1.5 inch diameter.
It suits fast or medium fast growing trees. Yews hate them and absolutely refused to put their roots below the soil line.
One of the best ways to use them is grow your trees in the ground (save all the hassle of watering etc - unless mega hot) then when you think it large enough undercut in September and lift it in March as the buds begin to swell. This time, instead of using a normal airpot use an airpot seed tray. This will promote lots of new fibrous roots, and usually, as the tree is brim full of energy from the ground, can be potted into a bonsai container the following year. You will be amazed at how many roots there are.
You can also use airpots in reverse which is how the horticultural industry use them. Grow your tree for a couple of years in an airpot and get lots of fibrous roots. Then plant in the ground. Because it has loads of roots it will grow faster, stronger and thicker than it would normally.

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